1. Field of the Invention
The present invention relates to an illumination apparatus, and a projection type display apparatus which modulates the output light from the illumination apparatus according to predetermined image information by using a light valve and projects thus modulated light onto a screen; and, in particular, to a configuration of an illumination apparatus comprising a plurality of light source sections.
2. Description of the Prior Art
Methods using a lens array or a lenticular plate have conventionally been known as an integrator type in illumination apparatus employed in projection type display apparatus. Even when a light source having uneven light-distributing characteristics such as a metal halide lamp, xenon lamp, or halogen lamp is used, this type of methods can yield an illumination apparatus which can eliminate the unevenness in illumination on the light valve caused by light-distributing characteristics of the light source.
Such an illumination apparatus comprises a first integrator plate (known as a second flyeye or the like in general) and a second integrator plate (known as a first flyeye or the like in general) successively disposed in this order downstream a light source section using a reflector. The first integrator plate is constituted by a plurality of two-dimensionally arranged lens elements, each having a form substantially similar to that of the liquid crystal display panel. A luminous flux with a large unevenness in brightness emitted from the light source section is divided by the first integrator plate into partial luminous fluxes whose number is identical to the number of lens elements in the first integrator plate. The unevenness in brightness of partial luminous fluxes is smaller than that of the undivided luminous flux. The partial luminous fluxes form respective secondary light sources on the surface of the second integrator plate (which becomes conjugate with the pupil surface of a projection lens), which are emitted toward the illuminating region by way of the second integrator plate and a field lens, so as to be superposed on each other, whereby illumination with a smaller unevenness in brightness can be realized.
Known as the projection type display apparatus using two integrator plates as mentioned above is one having a plurality of light sources arranged symmetrical about the optical axis in order to secure the quantity of illumination light, and so forth (Japanese Unexamined Patent Publication No. 6-265887).
In the case of an illumination apparatus comprising a single light source, the unevenness in illumination caused by light-distributing characteristics of the light source can effectively be eliminated by the above-mentioned integrator type. In an illumination apparatus in which a plurality of light sources are arranged symmetrical about the optical axis, however, a new intensity distribution occurs due to light-distributing characteristics of the light sources. Namely, since individual light sources having respective intensity distributions different from each other are arranged symmetrical about the optical axis, a part having a high intensity occurs at a position not near the optical axis but separated from the optical axis by a predetermined distance on the pupil surface of the projection lens, which becomes conjugate with the surface of the second integrator plate. However, the imaging performance of the projection lens is higher in the vicinity of the optical axis and becomes lower as being distanced further therefrom. If a part having a higher intensity, i.e., a part governing the imaging performance, exists at a position separated from the optical axis on the pupil surface by a predetermined distance as mentioned above, it becomes harder to fully exhibit the imaging performance inherent in the projection lens.
A conventional example which can deal with such a problem caused by a plurality of light sources is the illumination apparatus and the projection type display apparatus using the same disclosed in Japanese Unexamined Patent Publication No. 2000-3612. This illumination apparatus comprises a plurality of light source sections each comprising an ellipsoidal mirror having a first focal point near the center of gravity of a luminous body, whereas the luminous flux from each light source section is reflected toward the integrator by a reflecting prism having a reflecting surface near a second focal point of each ellipsoidal mirror. Therefore, the secondary light source of luminous body formed on the reflecting surface of the reflecting prism is located nearer to the optical axis of the illumination apparatus than is the luminous body itself, whereby the position of the secondary light source can be taken as the light source position in its downstream optical systems. Thus, while this apparatus is a bright illumination apparatus comprising a plurality of light sources, a light spot is formed by the luminous flux from each light source section at a position near the optical axis on the pupil surface of the projection lens, whereby the imaging performance of the projection lens can be made favorable.
However, the apparatus mentioned above aims at improving the uniformity in illuminance and color of the illumination light. Therefore, it is considered important for luminous body images formed on the projection lens pupil surface to be arranged substantially symmetrical about the optical axis even when a plurality of lamps are used. Namely, the luminous body images are arranged substantially symmetrical about the optical axis, whereby the light spot formed by the luminous flux from each light source section is resultantly positioned near the optical axis. Hence, this apparatus is not necessarily conceived to cause the above-mentioned projection lens to fully exhibit its imaging performance.
As mentioned above, the imaging performance of projection lens is higher in the vicinity of the optical axis and becomes lower as being separated farther therefrom. Therefore, in order to utilize the imaging performance of the projection lens most effectively, it is desirable that the part having a higher luminous flux intensity be transmitted through the pupil surface of the projection lens at a position as close to the optical axis as possible. Though the light spot formed by the luminous flux from each light source section can be formed at a position close to the optical axis to a certain extent in this conventional example, there is a limit. Namely, as the light spot approaches the optical axis, the position at which the luminous flux from the light source section is reflected on each reflecting surface of the reflecting prism inevitably approaches a vertex of the reflecting prism formed by reflecting surfaces of the reflecting prism. However, a certain area is necessary for reflecting a luminous flux even in the vicinity of the focal position of the luminous flux, whereby no luminous flux can be reflected by a vertex of the reflection prism.
Therefore, a paradigm shift is necessary for causing the part with a higher intensity of the luminous flux from a light source section to pass through the pupil surface of the projection lens at a position nearer to the optical axis, and further effectively utilizing the imaging performance of the projection lens.
Commonly assigned Japanese Unexamined Patent Publication No. 11-44920 discloses a projection type display apparatus proposed as one solving the above-mentioned problem caused by a plurality of light sources. This projection type display apparatus is configured such that the luminous fluxes from each light source section is moved in an integrator section so as to approach the optical axis of the integrator section while the rate of change in the distance from the luminous flux center to the optical axis becomes the rate of change in the diameter of the luminous flux or greater. As a consequence, in the pupil surface of the projection lens, the light spot caused by the luminous flux from each light source section is formed at a position near the optical axis, whereby the imaging performance of the projection lens can be made favorable.
In this conventional example, the luminous flux from each light source section is moved as mentioned above in the integrator section. Specifically, two wedge-like prisms are disposed in the integrator section or each of the lenses constituting the flyeye is shaped into a wedge-like prism itself, whereby the effects mentioned above can be obtained.
In view of such circumstances, it is an object of the present invention to provide an illumination apparatus which can easily be made smaller and can cause the projection lens to fully exhibit the imaging performance inherent therein by placing the part with a higher light intensity corresponding to each light source as nearer to the optical axis of the illumination apparatus as possible when a plurality of light sources are arranged symmetrical about the optical axis while the illumination light is homogenized by the integrator type.
Also, in a similar case, it is an object of the present invention to provide, in a configuration easier to assemble at a lower cost as compared with conventional ones, an illumination apparatus which can cause the projection lens to fully exhibit the imaging performance inherent therein by placing the part with a higher light intensity corresponding to each light source nearer to the optical axis of the illumination apparatus on the surface of the second integrator plate, which is conjugate with the pupil surface of the projection lens.
It is another object of the present invention to provide a projection type display apparatus comprising the above-mentioned illumination apparatus.
The present invention provides an illumination apparatus comprising:
a light source group in which a plurality of light source sections, each constituted by a luminous body and a reflector comprising an ellipsoidal surface having one focal point located near a center of gravity of the luminous body, are arranged;
an integrator section, constituted by at least two integrator plates, for homogenizing a quantity of light emitted from the light source group, the integrator section being arranged in an optical axis direction of the light; and
at least one mirror element, having a reflecting surface near the other focal point of the ellipsoidal surface of at least one reflector, for reflecting a luminous flux from the light source group toward the integrator section;
wherein the illumination apparatus as a whole has an optical axis forming a predetermined angle with an optical axis of the at least one reflector.
Preferably, at least one lens for emitting the luminous flux from the mirror element toward the integrator section as a substantially parallel luminous flux is disposed on the mirror element side of the integrator section.
Preferably, the lens is formed integrally with the integrator plate on the mirror element side in the integrator section on the surface of the integrator plate facing the mirror element.
The lens may be formed integrally with the integrator plate from a plastic material. Preferably, the lens has an aspheric surface.
The light source group may comprise at least two light source sections arranged such that respective luminous fluxes therefrom are incident on the lens at an angle by which a center axis of each of the luminous fluxes substantially intersects the optical axis of the lens.
The light source group may comprise at least two light source sections, whereas the mirror element has a reflecting surface near the other focal point of the ellipsoidal surface of each of the reflectors of the two light source sections so as to reflect the luminous flux from the light source group toward the integrator section.
The present invention provides a projection type display apparatus comprising the above-mentioned illumination apparatus, a light valve for modulating output light from the integrator section according to predetermined image information, and a projection lens for projecting onto a screen an optical image formed by the light modulated by the light valve.
Here, xe2x80x9cthe illumination apparatus as a whole has an optical axis forming a predetermined angle with the optical axis of the at least one reflectorxe2x80x9d indicates that, in a state where the luminous flux from the reflector is assumed to be focused once and then become incident on the integrator section while being kept on linearly advancing without the mirror element, the optical axis of the illumination apparatus as a whole and the optical axis of the reflector have such an angle therebetween that the distance from the optical axis of the whole illumination apparatus to the center of gravity of the luminous body is greater than the distance from the optical axis of the whole illumination apparatus to the focal point. Namely, in thus assumed state, the optical axis of the reflector intersects the optical axis of the whole illumination apparatus on its extension directed to the focal point.
The present invention provides an illumination apparatus comprising:
a light source group in which a plurality of light source sections, each constituted by a luminous body and a reflector comprising a parabolic surface for emitting a luminous flux from the luminous body to a front side of an optical axis, are arranged;
an integrator section, constituted by at least two integrator plates, for homogenizing in a cross section perpendicular to the optical axis a quantity of light emitted from the light source group, the integrator section being arranged in the optical axis direction; and
a parallel luminous flux approaching optical system comprising a plurality of first lens groups corresponding to the plurality of light source sections in the light source group substantially one by one and functioning to cause each of the luminous fluxes from the plurality of light source sections to form a focal point once; and at least one second lens group, disposed downstream the focal point, for emitting the luminous fluxes from the light source group toward the integrator section as a substantially parallel luminous flux;
wherein the optical axis of the whole illumination apparatus and optical axes of the light source section and first lens group forming a pair are substantially parallel to each other and satisfy the following conditional expression (1):
Saxis greater than Faxisxe2x80x83xe2x80x83(1) 
where
Saxis is the distance between the optical axis of the whole illumination apparatus and the optical axis of the light source section; and
Faxis is the distance between the optical axis of the whole illumination apparatus and the optical axis of the first lens group.
Preferably, at least one mirror element, having a reflecting surface near at least one of the plurality of focal points caused by the plurality of first lens groups, for reflecting a luminous flux toward the second lens group is provided.
Preferably, the light source group comprises two light source sections, whereas the mirror element having reflecting surfaces near two focal points caused by the first lens groups corresponding to the light source sections one by one is provided.
Preferably, each of at least one first lens group and at least one second lens group is constituted by a single lens having substantially the same form. Preferably, at least one of the first and second lens groups is made of a single aspherical lens.
Preferably, at least one second lens group is integrally formed with the integrator plate on the light source group side in the integrator section at the surface thereof on the light source group side.
The present invention provides a projection type display apparatus comprising the above-mentioned illumination apparatus, a light valve for modulating output light from the integrator section according to predetermined image information, and a projection lens for projecting onto a screen an optical image formed by the light modulated by the light valve.
Here, the expression xe2x80x9cthe optical axis of the whole illumination apparatus and optical axes of the light source section and first lens group forming a pair are substantially parallel to each otherxe2x80x9d mentioned above refers to the case where the optical axis of the whole illumination apparatus, the optical axis of the light source section, and the optical axis of the first lens group corresponding to the light source section are substantially parallel to each other in a state where it is assumed that the positions of the light source section and the first lens group corresponding thereto would be located where the luminous flux from the light source section advances straightforward by way of the first lens group so as to be made incident on the second lens group and the integrator section with the mirror element being removed, if the luminous flux from the light source section is bent toward the second lens group due to the insertion of the mirror element.